Nowadays, consumer electronics, like toys, mobile phones, tablet computers, and remote controls, are gradually developed to be more intellective. More sensors are contained to perceive more physical quantities. Specifically, the demand for the measurement of stress or pressure generated by human body (especially fingers) gradually increased.
Some special requirements are proposed for the sensors used for the measurement of stress or pressure. Firstly, stress or pressure should be transmitted onto the sensing film effectively; secondly, the sensing film, wires and other parts of a pressure sensing chip should be protected from damage; thirdly, the size of the pressure sensor should be small to meet the growing miniaturization trend of consumer electronics.
Although the producing process of a prior pressure sensing chip with a sensing film has been mature, the sensing film has some disadvantages on the measurement of stress or pressure. Firstly, the sensing film, the thickness of which is normally tens of microns or less, can only be competent for the measurement of fluid pressure; and is easily damaged by external physical pressure generated by human body especially fingers. Secondly, wires, used in a package structure of a prior pressure sensor, are normally exposed above the sensing film. In this case, the wires are also easily damaged if directly touched by human body or fingers. The prior approach to solve above problems is isolating the sensing film through the package structure, by which the pressure generated by human body is converted to fluid pressure on the sensing film. However, the prior package structure may be overprotective and too large, in which the pressure generated by human body cannot be effectively transmitted onto the sensing film; or, the prior package structure cannot adequately protect those easily damaged parts of the pressure sensing chip at all. Furthermore, the prior packaging processes are too complicated.
A packaging method for protecting the sensing film of a pressure sensor chip is disclosed in U.S. Pat. No. 6,401,545, in which a dam is constructed to isolate different parts of the pressure sensor chip. The sensing film is located at one side of the dam, and a kind of soft material is prepared on the sensing film to ensure pressure transmitting. A kind of hard material is prepared to protect the bonding pads and wires around the pressure sensor chip. However, the constructing process of the dam is complicated, and the soft material may still damage the sensing film during transmitting the pressure onto the sensing film.
Another packaging method is disclosed in U.S. Pat. No. 7,148,881, in which a cavity is formed around a pressure sensor. When external force is exerted on the cavity, the pressure change generated by the deformation of the cavity is transmitted to the sensing film. The disadvantage of this method is that the packaging process is complicated and the package structure is too large.
Another package structure is disclosed in China Patent Pat. No. ZL200810021732.3, in which different materials are used in different regions of the pressure sensor, and a pressure transmitting method is proposed for transmitting force and the protection of bonding pads and wires. However, three kinds of material are required in this package structure, which makes the packaging process too complicated.